Certain electronic applications, such as OLED display back panels, require small islands of high-quality semiconductor material distributed over a large area. This area can be 50 inches diagonally and larger, and exceeds the sizes of crystalline semiconductor wafers that can be fabricated using the traditional boule-based techniques.
WO 2013/053052 A1, incorporated herein by reference, discloses fabricating a large number of small, loose, crystalline semiconductor spheres. The spheres are then distributed on a patterned substrate and affixed to the substrate at predetermined locations to form an array of spheres on the substrate. Planarizing the spheres exposes a cross-section of each sphere, thereby providing an array of high-quality, crystalline semiconductor islands for device fabrication on a globally planarized surface.
U.S. Pat. No. 4,637,855, incorporated herein by reference, discloses fabricating spheres of silicon on a substrate by applying a slurry of metallurgical grade silicon to the substrate and then patterning the slurry layer to provide regions of metallurgical silicon of uniform size. The substrate is then heated to melt the silicon, which then beads to the surface to form molten spheres of silicon, which are then cooled to crystallize them. The spheres have very weak adhesion to the substrate and are easily detached from the substrate by simply knocking them loose. The loose spheres are collected and undergo further processing.
US 2012/0067273 A1, incorporated herein by reference, discloses fabricating silicon wafers by bringing a substrate into contact with a reservoir of molten silicon, forming a layer of solid silicon on the substrate, and subsequently detaching the solid layer from the substrate. The disclosed method can potentially be used to fabricate silicon wafers with large areas.